The problem of composition shift in zeotropic fluid circulation, which is encountered in modern air conditioning and refrigeration systems, is studied. It reveals that the composition shift phenomena is contributed by...The problem of composition shift in zeotropic fluid circulation, which is encountered in modern air conditioning and refrigeration systems, is studied. It reveals that the composition shift phenomena is contributed by fractionation related to four mechanisms. This paper concentrates on the modeling of component fractionation in heat exchangers. Element approach is employed, and the amount of each component holdup is calculated element by element with a proper void fraction model. The circulation concentration is determined from the refrigerant differential holdup in heat exchangers. Simulations are carried out to prove the validity. The results can improve the reliability and efficiency in zeotropic refrigerant applications.展开更多
The isotope effects of XF （X=H, D） on the population transfer process via two-photon resonance excitation are investigated by solving the time-dependent SchrSdinger equation. The vibrational levels v=0 and 2 of the ...The isotope effects of XF （X=H, D） on the population transfer process via two-photon resonance excitation are investigated by solving the time-dependent SchrSdinger equation. The vibrational levels v=0 and 2 of the ground electronic state are taken to be the initial and target states, respectively, for the two molecular systems. The influences of the field peak amplitude and pulse duration on the population transfer process are discussed in detail. The pulse duration is required to be longer than 860 fs for the DF molecule to achieve a relatively high transfer probability （more than 80%）, while the one for the HF molecule is just required to be longer than 460 fs. Moreover, the intermediate level v=1 and the higher level v=3 may play more important roles in the two-photon resonance process for the DF molecule, compared to the roles in the process for the HF molecule.展开更多
该文针对基于共源共栅氮化镓高电子迁移率晶体管(Cascode GaN HEMT)的直流固态功率控制器(SSPC)在开通过程中的振荡问题,利用Spice模型与Q3D软件提取Cascode结构内部寄生参数,结合SSPC实际工作情况和Cascode结构对开通和关断过程进行分...该文针对基于共源共栅氮化镓高电子迁移率晶体管(Cascode GaN HEMT)的直流固态功率控制器(SSPC)在开通过程中的振荡问题,利用Spice模型与Q3D软件提取Cascode结构内部寄生参数,结合SSPC实际工作情况和Cascode结构对开通和关断过程进行分析,在Saber软件中对SSPC开通过程进行仿真分析。仿真结果表明,振荡产生的主要原因是,在SSPC开通过程中,Cascode GaN HEMT长时间工作在饱和区,容易受到外界干扰产生振荡,且内部存在正反馈环路。针对该问题,该文提出并联RC吸收电路和增大门级驱动电阻的方案,实验结果表明,所提出的方案可以有效抑制振荡。展开更多
A technology for the monolithic integration of resonant tunneling diodes （RTDs） and high electron mobility transistors （HEMTs） is developed. Molecular beam epitaxy is used to grow an RTD on a HEMT structure on GaA...A technology for the monolithic integration of resonant tunneling diodes （RTDs） and high electron mobility transistors （HEMTs） is developed. Molecular beam epitaxy is used to grow an RTD on a HEMT structure on GaAs substrate. The RTD has a room temperature peak-to-valley ratio of 5.2 ： 1 with a peak current density of 22. 5kA/cm^2. The HEMT has a 1μm gate length with a - 1V threshold voltage. A logic circuit called a monostable-to-bistable transition logic element （MOBILE） circuit is developed. The experimental result confirms that the fabricated logic circuit operates successfully with frequency operations of up to 2GHz.展开更多
文摘The problem of composition shift in zeotropic fluid circulation, which is encountered in modern air conditioning and refrigeration systems, is studied. It reveals that the composition shift phenomena is contributed by fractionation related to four mechanisms. This paper concentrates on the modeling of component fractionation in heat exchangers. Element approach is employed, and the amount of each component holdup is calculated element by element with a proper void fraction model. The circulation concentration is determined from the refrigerant differential holdup in heat exchangers. Simulations are carried out to prove the validity. The results can improve the reliability and efficiency in zeotropic refrigerant applications.
文摘The isotope effects of XF （X=H, D） on the population transfer process via two-photon resonance excitation are investigated by solving the time-dependent SchrSdinger equation. The vibrational levels v=0 and 2 of the ground electronic state are taken to be the initial and target states, respectively, for the two molecular systems. The influences of the field peak amplitude and pulse duration on the population transfer process are discussed in detail. The pulse duration is required to be longer than 860 fs for the DF molecule to achieve a relatively high transfer probability （more than 80%）, while the one for the HF molecule is just required to be longer than 460 fs. Moreover, the intermediate level v=1 and the higher level v=3 may play more important roles in the two-photon resonance process for the DF molecule, compared to the roles in the process for the HF molecule.
文摘该文针对基于共源共栅氮化镓高电子迁移率晶体管(Cascode GaN HEMT)的直流固态功率控制器(SSPC)在开通过程中的振荡问题,利用Spice模型与Q3D软件提取Cascode结构内部寄生参数,结合SSPC实际工作情况和Cascode结构对开通和关断过程进行分析,在Saber软件中对SSPC开通过程进行仿真分析。仿真结果表明,振荡产生的主要原因是,在SSPC开通过程中,Cascode GaN HEMT长时间工作在饱和区,容易受到外界干扰产生振荡,且内部存在正反馈环路。针对该问题,该文提出并联RC吸收电路和增大门级驱动电阻的方案,实验结果表明,所提出的方案可以有效抑制振荡。
文摘A technology for the monolithic integration of resonant tunneling diodes （RTDs） and high electron mobility transistors （HEMTs） is developed. Molecular beam epitaxy is used to grow an RTD on a HEMT structure on GaAs substrate. The RTD has a room temperature peak-to-valley ratio of 5.2 ： 1 with a peak current density of 22. 5kA/cm^2. The HEMT has a 1μm gate length with a - 1V threshold voltage. A logic circuit called a monostable-to-bistable transition logic element （MOBILE） circuit is developed. The experimental result confirms that the fabricated logic circuit operates successfully with frequency operations of up to 2GHz.
